Manufacturing a printhead that has relatively high resolution and print-speed raises a number of problems. Difficulties in manufacturing pagewidth printheads of any substantial size arise due to the relatively small dimensions of standard silicon wafers that are used in printhead (or printhead module) manufacture. For example, if it is desired to make an 8 inch wide pagewidth printhead, only one such printhead can be laid out on a standard 8-inch wafer, since such wafers are circular in plan.
Manufacturing a pagewidth printhead from two or more smaller modules can reduce this limitation to some extent, but raises other problems related to providing a joint between adjacent printhead modules that is precise enough to avoid visible artefacts (which would typically take the form of noticeable lines) when the printhead is used. The problem is exacerbated in relatively high-resolution applications because of the tight tolerances dictated by the small spacing between nozzles.
The quality of a joint region between adjacent printhead modules relies on factors including a precision with which the abutting ends of each module can be manufactured, the accuracy with which they can be aligned when assembled into a single printhead, and other more practical factors such as management of ink channels behind the nozzles. It will be appreciated that the difficulties include relative vertical displacement of the printhead modules with respect to each other.
Whilst some of these issues may be dealt with by careful design and manufacture, the level of precision required renders it relatively expensive to manufacture printheads within the required tolerances. It would be desirable to provide a solution to one or more of the problems associated with precision manufacture and assembly of multiple printhead modules to form a printhead, and especially a pagewidth printhead.
In some cases, it is desirable to produce a number of different printhead module types or lengths on a substrate to maximise usage of the substrate's surface area. However, different sizes and types of modules will have different numbers and layouts of print nozzles, potentially including different horizontal and vertical offsets. Where two or more modules are to be joined to form a single printhead, there is also the problem of dealing with different seam shapes between abutting ends of joined modules, which again may incorporate vertical or horizontal offsets between the modules. Printhead controllers are usually dedicated application specific integrated circuits (ASICs) designed for specific use with a single type of printhead module, that is used by itself rather than with other modules. It would be desirable to provide a way in which different lengths and types of printhead modules could be accounted for using a single printer controller.
Printer controllers face other difficulties when two or more printhead modules are involved, especially if it is desired to send dot data to each of the printheads directly (rather than via a single printhead connected to the controller). One concern is that data delivered to different length controllers at the same rate will cause the shorter of the modules to be ready for printing before any longer modules. Where there is little difference involved, the issue may not be of importance, but for large length differences, the result is that the bandwidth of a shared memory from which the dot data is supplied to the modules is effectively left idle once one of the modules is full and the remaining module or modules is still being filled. It would be desirable to provide a way of improving memory bandwidth usage in a system comprising a plurality of printhead modules of uneven length.
In any printing system that includes multiple nozzles on a printhead or printhead module, there is the possibility of one or more of the nozzles failing in the field, or being inoperative due to manufacturing defect. Given the relatively large size of a typical printhead module, it would be desirable to provide some form of compensation for one or more “dead” nozzles. Where the printhead also outputs fixative on a per-nozzle basis, it is also desirable that the fixative is provided in such a way that dead nozzles are compensated for.
A printer controller can take the form of an integrated circuit, comprising a processor and one or more peripheral hardware units for implementing specific data manipulation functions. A number of these units and the processor may need access to a common resource such as memory. One way of arbitrating between multiple access requests for a common resource is timeslot arbitration, in which access to the resource is guaranteed to a particular requestor during a predetermined timeslot.
One difficulty with this arrangement lies in the fact that not all access requests make the same demands on the resource in terms of timing and latency. For example, a memory read requires that data be fetched from memory, which may take a number of cycles, whereas a memory write can commence immediately. Timeslot arbitration does not take into account these differences, which may result in accesses being performed in a less efficient manner than might otherwise be the case. It would be desirable to provide a timeslot arbitration scheme that improved this efficiency as compared with prior art timeslot arbitration schemes.
Also of concern when allocating resources in a timeslot arbitration scheme is the fact that the priority of an access request may not be the same for all units. For example, it would be desirable to provide a timeslot arbitration scheme in which one requestor (typically the memory) is granted special priority such that its requests are dealt with earlier than would be the case in the absence of such priority.
In systems that use a memory and cache, a cache miss (in which an attempt to load data or an instruction from a cache fails) results in a memory access followed by a cache update. It is often desirable when updating the cache in this way to update data other than that which was actually missed. A typical example would be a cache miss for a byte resulting in an entire word or line of the cache associated with that byte being updated. However, this can have the effect of tying up bandwidth between the memory (or a memory manager) and the processor where the bandwidth is such that several cycles are required to transfer the entire word or line to the cache. It would be desirable to provide a mechanism for updating a cache that improved cache update speed and/or efficiency.
Most integrated circuits an externally provided signal as (or to generate) a clock, often provided from a dedicated clock generation circuit. This is often due to the difficulties of providing an onboard clock that can operate at a speed that is predictable. Manufacturing tolerances of such on-board clock generation circuitry can result in clock rates that vary by a factor of two, and operating temperatures can increase this margin by an additional factor of two. In some cases, the particular rate at which the clock operates is not of particular concern. However, where the integrated circuit will be writing to an internal circuit that is sensitive to the time over which a signal is provided, it may be undesirable to have the signal be applied for too long or short a time. For example, flash memory is sensitive to being written too for too long a period. It would be desirable to provide a mechanism for adjusting a rate of an on-chip system clock to take into account the impact of manufacturing variations on clockspeed.